# Thread: "Observable universe" vs actual universe

1. Originally Posted by dapifo
During all the thread I was assuming that the Whole Universe starts also in the Big-bang 13,7 billions years ago....then I didnīt understand how it could expand so much (till near infinite).
I don't see why not; doesn't it just depend how big it was to start with?

Now I realize that you accept that is possible that Our Universe started in the Big-bang 13,7 billions years ago....inside other older and larger Whole Universe
That is possible, but I don't think it is the generally accepted model. It sounds like a version of the "eternal inflation" model: http://en.wikipedia.org/wiki/Eternal_inflation

and now I understand about the m1omg phrase: "Our universe is probably so big that it contains a near infinite number of your identical twin, doing the exact same thing as you are doing right now.".....That there will be so many (near infinites) bubbles like Our Universe..that it is probabilistically possible that one could exact to Our Universe.
I don't think that is what he meant; I assumed he meant within the (one) universe.

Currently we don't have any evidence for multiple big bangs, bubble universe, anything existing before the big bang, etc. So any ideas are pretty much speculative at the moment.

2. Originally Posted by m1omg
[...] if you said that the actual universe is as large compared to the observable universe as the observable universe is compared to a single Planck volume, you'd be underestimating the size of the universe by more than a factor of googolplex.[...]
Planck Dimension= 10^-35 meter
Observable Universe = 10^+26 meters = 10^60 Planck Dimension

If actual universe is as large compared to the observable universe as the observable universe is compared to a single Planck volume, then:

actual universe = 10^95 meters....near Googol meters....not Googolplex (!!!)

If actual universe = 1 Googolplex meters= 10^(10^100) meters...then will be = near 10^(10^98) times Our Observable Universe (!!!)

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And if the universe is actually carried on the backs of turtles 10^700 metres across then the universe is 10^674 times larger than our observed universe.

I don't get why you are just spraying out random numbers here. Why should the universe care about base 10?

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Originally Posted by dapifo
During all the thread I was assuming that the Whole Universe starts also in the Big-bang 13,7 billions years ago....then I didnīt understand how it could expand so much (till near infinite).
This is one of the things that people tend not to get about the Big Bang - it was not an explosion as we experience in everyday life. The universe did not expand into anything to get bigger.
Frequently Asked Questions in Cosmology: What is the Universe expanding into?

It was an expansion in spacetime which did not change the size of the universe. The universe is usually considered be infinitely big (no limits to its size).
What is changing are distances within the universe.

5. Originally Posted by Shaula
And if the universe is actually carried on the backs of turtles 10^700 metres across then the universe is 10^674 times larger than our observed universe.

I don't get why you are just spraying out random numbers here. Why should the universe care about base 10?
m1omg did...

6. Originally Posted by Reality Check
It was an expansion in spacetime which did not change the size of the universe. The universe is usually considered be infinitely big (no limits to its size).What is changing are distances within the universe.
That , if it is true, is new for me!!!...It is very interesting !!!

Then the universe allready exist before the Big-bang... with the same size than now.....and the only change "after the Big-bang" were the distances within the universe (!!!??)

I donīt understand....!!!

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Originally Posted by dapifo
Then the universe allready exist before the Big-bang... with the same size than now.....and the only change "after the Big-bang" were the distances within the universe (!!!??)
Or maybe the universe did not exist before the Big Bang.
Or maybe the universe had a different "size" before the Big Bang.
All we know is that there was a Big Bang and that the universe did not change its size. It stays as infinite if it is infinite. It stays as finite if finite.

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The Big Bang theory only states that the observable universe grew from a hot dense state finite time ago. It says very little about the wider universe, it says very little about the state of the observable universe before the point in time where the model breaks down.

m1omg did...
He mentioned some bounds from inflationary models. That is all they are. You just seemed to be making up numbers and linking them with "if then if then if" statements.

9. Originally Posted by Reality Check
All we know is that there was a Big Bang and that the universe did not change its size. It stays as infinite if it is infinite. It stays as finite if finite.
That is accepted by mainstream?

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Originally Posted by dapifo
That is accepted by mainstream?
Not really. Because as I said ... We do not know. There is a cut-off beyond which we just don't know. Go back far enough and we do not know. Statements that we do are based on what could be faulty extrapolations beyond the point at which we have a working theory.

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Arguments against exact duplicates in an infinite universe;

"Exact duplicate" involves not only the state of an object at a particular moment in time, but would involve the history of the object.
The history of an object is in part determined by its surroundings. So for there to be exact duplicates there must be exact duplicates of entire regions of the universe, with the exact same history. In fact it must be a pattern of repeating duplicate regions such that the effect that those regions have on one another is identical.

Additional argument: an infinite universe contains an infinite amount of matter/energy, which allows for infinite variation of the composition of objects. So an infinite universe does not inevitably lead to duplicate objects.

12. Originally Posted by Reality Check
It was an expansion in spacetime which did not change the size of the universe.
Your wording seems to be a bit misleading. It is normally said that it was an expansion OF spacetime, not in spacetime. And of course the "size" of the universe is getting bigger. If it's expanding, how could it not be getting bigger? An infinite universe (unknown to be the case) does not mean it has any particular size. It means, AFAIK, as time goes on, whatever size it is increases without end. The amount of baryonic and dark matter in the universe is apparently finite. No more of this stuff is appearing within the universe. As space continues to expand, the density of matter continues to decrease. This would seem to argue against "exact duplicates" in some distant region of the universe. Even if the "whole universe" is 1023 times larger than the portion that is visible to us, as Alan Guth originally estimated, that is nowhere near the size required to run into a duplicate of our galaxy, which, per Tegmark, is more like 101028 meters from here.

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Originally Posted by Cougar
Your wording seems to be a bit misleading. It is normally said that it was an expansion OF spacetime, not in spacetime.
Thanks for the correction.

Originally Posted by Cougar
And of course the "size" of the universe is getting bigger. If it's expanding, how could it not be getting bigger?
Not really. You are thinking about an expansion IN spacetime, e.g an explosion.
Infinity is the concept of being without bounds. Think about a set of numbers that is infinite:
What happens if you add a another item to the set? It is still infinite.
What happens if you add an infinite number of items to the set? It is still infinite.
Basically if you treat infinity as a number then it has strange properties, e.g. add 1 and it is still infinity , multiple by infinity and it is still infinity.
See Hilbert's paradox of the Grand Hotel.

So an infinite universe that is expanding still is infinite, i.e. its "size" does not change.
You have more space and so the density of matter decreases.

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Originally Posted by dapifo
That is accepted by mainstream?
Yes: If infinite then the size of the universe remains as infinite. If finite then the size of the universe remains as finite (but increasing AFAIK).

15. Originally Posted by Reality Check
What happens if you add a another item to the set? It is still infinite.
I hate infinity.

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Originally Posted by primummobile
Not really. There aren't an infinite number of things you could do. There would be infinite copies of you who slapped their face, and infinite almost-copies of you who did not.
Q tells me all my other selves are just as broke as me.

We can't win.

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